Australia's national security agency is investigating hundreds of its citizens for allegedly fighting in the conflict in Syria.

The government fears it may pose a security risk to Australia.

The head of the Australian Security Intelligence Organisation expressed his concern at the number of people who may be "radicalised" in "extremist doctines" and learn "skills terrorists could use" on their return to Australia. 

Al Jazeera's Andrew Thomas reports from Sydney.

Source: Al Jazeera